Microscope objective lens system

ABSTRACT

A low magnification microscope objective lens system which comprises a small number of lenses and wherein lateral chromatic aberration is controlled to a level similar to that in high magnification microscope objective lens systems while maintaining flatness of image.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a microscope objective lens systemdesigned for low magnification on the order of 10x.

(B) Description of the Prior Art

Conventional microscope objective lens systems designed for lowmagnification, especially on the order of 10x and improved flatness ofimage comprise a large number of lens elements and have short workingdistance (W.D.). Further, lateral chromatic aberration is aggravated andcan hardly be corrected in miscrocope objective lens systems for highmagnification levels though such aberration can be favorably correctedrelatively easily in microscope objective lens systems for lowmagnification levels. For this reason, lateral chromatic aberration isnot corrected in high magnification microscope objective lens systemsand is corrected later by eyepieces so that such aberration is favorablycorrected in the entire optical systems of microscopes. When a lowmagnification objective lens system is used in combination with aneyepiece so designed as to correct lateral chromatic aberration producedby a high magnification microscope objective lens system, lateralchromatic aberration will unavoidably be produced in the reversedirection.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a lowmagnification microscope lens system comprising a small number of lenselements, assuring improved flatness of image and producing lateralchromatic aberration on the order similar to that in high magnificationmicroscope objective lens systems.

The microscope objective lens system according to the present inventioncomprises a first positive lens, a second positive meniscus lens, athird negative lens, a fourth positive meniscus lens and a fifthpositive lens. Said objective lens system satisfies the conditionsdefined below:

    ______________________________________                                        (1)         0.3F < r.sub.3 < 1.2f                                             (2)         -0.5f < r.sub.5 < -0.15f                                          (3)         0.15f < d.sub.4 < 0.5f                                            (4)                                                                                        ##STR1##                                                         (5)         | ν.sub.1 - ν.sub.2 | < 10 ,                          | n.sub.1 - n.sub.2 | > 0.05                    (6)         0.5f < | r.sub.1 | < 4f                         ______________________________________                                    

Wherein the reference symbols represent as follows: r₁, r₃, r₅ : radiiof curvature on the respective object side surfaces of the first, secondand third lenses d₄ : airspace between the second and third lenses d₆ :airspace between the third and fourth lenses d₅, d₇ : thicknesses of thethird and fourth lenses respectively n₁, n₂, n₃, n₄ : refractive indicesof the first, second, third and fourth lenses respectively ν₁, ν₂ :Abbe's numbers of the first and second lenses respectively f: focallength of the entire lens system as a whole

Now, the significance of the afore-mentioned conditions will bedescribed below: The conditions (1) and (2) are adopted for favorablycorrecting spherical aberration and coma while maintaining curvature offield at a desirable level. That is to say, aforesaid aberrations arefavorably corrected by selecting a meniscus lens as the second elementand so designing the third lens as to have a strongly concave surface r₅on the object side. If either one of r₃ and r₅ is smaller than the lowerlimit of the conditions (1) or (2), it will be difficult to correctcurvature of field and it will be impossible to maintain favorableflatness of image. When r₃ or r₅ exceeds the upper limit of thecondition (1) or (2), in contrast, it will be impossible to favorablycorrect spherical aberration and coma.

The condition (3) is effective mainly for correcting coma favorably. Ifd₄ is smaller than the lower limit defined by the condition (3), comaand astigmatic difference will be overcorrected. If d₄ is larger thanthe upper limit of the condition (3), however, proper balance will belost among various aberrations.

The conditions (4) and (5) are adopted for favorably correctingspherical aberration while maintaining lateral chromatic aberration at adegree similar to that in high magnification microscope objective lenssystems. The lens system according to the present invention is sodesigned as to have an OSC' value larger than those of general objectivelens systems. That is to say, C line has an OSC' value of approx.0.24˜0.35% and F line has an OSC' value of approx. 0.56˜0.86. If d₅ /n₃+d₆ +d₇ /n₄ has a value larger than the upper limit defined by thecondition (4), it will be impossible to maintain proper balance incorrection of spherical aberration. If aforesaid value is smaller thanthe lower limit of the condition (4), in contrast, it will be impossibleto control lateral chromatic aberration to the level similar to that inhigh magnification objective lens systems. If |ν₁ -ν₂ | exceeds 10 inthe condition (5), it will be impossible to increase lateral chromaticaberration to the level similar to that in high magnification objectivelens systems. When |n₁ -n₂ | is smaller than 0.05 in the condition (4)in contrast, it will be impossible to favorably correct sphericalaberration while maintaining lateral chromatic aberration to a levelsimilar to that in high magnification objective lens systems. Finally,the condition (6) is required mainly for correcting spherical aberrationfavorably. If |r₁ | exceeds the upper limit of the condition (6), itwill be difficult to correct spherical aberration. If |r₁ | is smallerthan the lower limit of the condition (6), proper balance will be lostamong various aberrations, especially aggravating coma and astigmatism.

Furthermore, it is preferable to select a glass material having a highrefractive index and low dispersion for the third lens in order tomaintain favorable flatness of image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view illustrating the composition of the lenssystem accoreing to the present invention;

FIG. 2A through FIG. 2D show curves illustrating the aberrationcharacteristics of the Embodiment 1;

FIG. 3A through FIG. 3D show curves illustrating the aberrationcharacteristics of the Embodiment 2;

FIG. 4A through FIG. 4D illustrate graphs showing the aberrationcharacteristics of the Embodiment 3; and

FIG. 5A through FIG. 5D illustrate graphs showing the abeerationcharacteristics of the Embodiment 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, some preferred embodiments of the present invention will bedetailedly described below:

    ______________________________________                                        Embodiment 1                                                                  f = 1             NA = 0.25   β = -9.977                                 WD = 0.3980       Petzval sum 0.20                                            r.sub.1 = -1.6154                                                                        d.sub.1 = 0.0940                                                                         n.sub.1 = 1.72916                                                                         ν.sub.1 = 54.7                           r.sub.2 = -0.4890                                                                        d.sub.2 = 0.0281                                                   r.sub.3 = 0.3617                                                                         d.sub.3 = 0.1055                                                                         n.sub.2 = 1.64                                                                            ν.sub.2 = 60.2                           r.sub.4 = 1.0714                                                                         d.sub.4 = 0.4012                                                   r.sub.5 = -0.1965                                                                        d.sub.5 = 0.1307                                                                         n.sub.3 = 1.80518                                                                         ν.sub.3 = 25.4                           r.sub.6 = ∞                                                                        d.sub.6 = 0.0075                                                   r.sub.7 = -1.3286                                                                        d.sub.7 = 0.2132                                                                         n.sub.4 = 1.62299                                                                         ν.sub.4 = 58.2                           r.sub.8 = -0.4663                                                                        d.sub.8 = 0.0344                                                   r.sub.9 = -12.9551                                                                       d.sub.9 = 0.1399                                                                         n.sub.5 = 1.64250                                                                         ν.sub.5 = 58.4                           r.sub.10 = -0.6018                                                            Embodiment 2                                                                  f = 1             NA = 0.25   β = -9.999                                 WD = 0.4083       Petzval sum 0.2                                             r.sub.1 = -1.3336                                                                        d.sub.1 = 0.0964                                                                         n.sub.1 = 1.755                                                                           ν.sub.1 = 52.4                           r.sub.2 = -0.5108                                                                        d.sub.2 = 0.0296                                                   r.sub.3 = 0.3588                                                                         d.sub.3 = 0.1079                                                                         n.sub.2 = 1.64                                                                            ν.sub.2 = 60.2                           r.sub.4 = 1.1284                                                                         d.sub.4 = 0.3806                                                   r.sub.5 = -0.2050                                                                        d.sub.5 = 0.1332                                                                         n.sub.3 = 1.80518                                                                         ν.sub.3 = 25.4                           r.sub.6 = ∞                                                                        d.sub.6 = 0.0127                                                   r.sub.7 = -1.3245                                                                        d.sub. 7 = 0.2177                                                                        n.sub.4 = 1.62299                                                                         ν.sub.4 = 58.2                           r.sub.8 = -0.4754                                                                        d.sub.8 = 0.0289                                                   r.sub.9 = 36.3549                                                                        d.sub.9 = 0.1387                                                                         n.sub.5 = 1.6425                                                                          ν.sub.5 = 58.4                           r.sub.10 = -0.6668                                                            Embodiment 3                                                                  f = 1             NA = 0.25   β  = -10.0                                 WD = 0.4122       Petzual sum 0.25                                            r.sub.1 = 0.7385                                                                         d.sub.1 = 0.0976                                                                         n.sub.1 = 1.7725                                                                          υ.sub.1 = 49.6                      r.sub.2 = -0.8133                                                                        d.sub.2 = 0.0296                                                   r.sub.3 = 1.1096                                                                         d.sub.3 = 0.1065                                                                         n.sub.2 = 1.691                                                                           ν.sub.2 = 54.8                           r.sub.4 = 5.9537                                                                         d.sub.4 = 0.2661                                                   r.sub.5 = -0.2321                                                                        d.sub.5 = 0.1325                                                                         n.sub.3 =  1.84666                                                                        ν.sub.3 = 23.9                           r.sub.6 = ∞                                                                        d.sub.6 = 0.0138                                                   r.sub.7 = -0.4858                                                                        d.sub.7 = 0.2189                                                                         n.sub.4 = 1.618                                                                           ν.sub.4 = 63.4                           r.sub.8 = -0.3832                                                                        d.sub.8 = 0.0849                                                   r.sub.9 = 2.8955                                                                         d.sub.9 = 0.1159                                                                         n.sub.5 = 1.618                                                                           ν.sub.5 = 63.4                           r.sub.10 = -0.8358                                                            Embodiment 4                                                                  f = 1             NA = 0.25   β = -10.0                                  WD = 0.4187       Petzval sum 0.25                                            r.sub.1 = 3.6219                                                                         d.sub.1 = 0.0988                                                                         n.sub.1 = 1.7859                                                                          ν.sub.1 = 44.1                           r.sub.2 = -0.4897                                                                        d.sub.2 = 0.0305                                                   r.sub.3 = 0.3711                                                                         d.sub.3 = 0.1109                                                                         n.sub.2 = 1.6935                                                                          ν.sub.2 = 53.3                           r.sub. 4 = 0.3933                                                                        d.sub.4 = 0.2297                                                   r.sub.5 = -0.2429                                                                        d.sub.5 = 0.1368                                                                         n.sub.3 = 1.84666                                                                         ν.sub.3 = 23.9                           r.sub.6 = ∞                                                                        d.sub.6 = 0.0135                                                   r.sub.7 = -0.9266                                                                        d.sub.7 = 0.2235                                                                         n.sub.4 = 1.48749                                                                         ν.sub.4 = 70.1                           r.sub.8 = -0.3829                                                                        d.sub.8 = 0.0766                                                   r.sub.9 = 5.1828                                                                         d.sub.9 = 0.1497                                                                         n.sub.5 = 1.618                                                                           ν.sub.5 = 63.4                           r.sub.10 = -0.7975                                                            ______________________________________                                    

wherein the reference symbols r₁ through r₁₀ represent radii ofcurvature on the respective surfaces of the first through the fifthlenses, the reference symbols d₁ through d₉ designate thicknesses of therespective lenses and airsapaces therebetween and the reference symbolsν₁ through ν₅ denote Abbe's numbers of the respective lenses.

I claim:
 1. An objective lens system for microscopes comprising a first positive lens, a second positive meniscus lens, a third negative lens, a fourth positive meniscus lens and a fifth positive meniscus lens, and said lens system having the following numerical data:

    ______________________________________                                         f = 1         NA = 0.25    β = -9.977                                     WD = 0.3980         Petzval sum 0.20                                           ______________________________________                                         r.sub.1 = -1.6154                                                               d.sub.1 = 0.0940                                                                             n.sub.1 = 1.72916                                                                           ν.sub.1 = 54.7                                  r.sub.2 = -0.4890                                                               d.sub.2 = 0.0281                                                              r.sub.3 = 0.3617                                                                d.sub.3 = 0.1055                                                                             n.sub.2 = 1.64                                                                              ν.sub.2 = 60.2                                  r.sub.4 = 1.0714                                                                d.sub.4 = 0.4012                                                              r.sub.5 = -0.1965                                                               d.sub.5 = 0.1307                                                                             n.sub.3 = 1.80518                                                                           ν.sub.3 = 25.4                                  r.sub.6 = ∞                                                               d.sub.6 = 0.0075                                                              r.sub.7 = -1.3286                                                               d.sub.7 = 0.2132                                                                             n.sub.4 = 1.62299                                                                           ν.sub.4 = 58.2                                  r.sub.8 = -0.4663                                                               d.sub.8 = 0.0344                                                              r.sub.9 =  -12.9551                                                             d.sub.9 = 0.1399                                                                             n.sub.5 = 1.64250                                                                           ν.sub.5 = 58.4                                  r.sub.10 = -0.6018                                                             ______________________________________                                    

wherein the reference symbol f represents focal length of the entire lens system as a whole, the reference symbols r₁ through r₁₀ designate radii of curvature on the respective surfaces of the lenses, the reference symbols d₁ through d₉ denote thicknesses of the respective lenses and the airspace therebetween, the reference symbols n₁ through n₅ represent refractive indices of the respective lenses and the reference symbols ν₁ through ν₅ designate Abbe's numbers of the respective lenses.
 2. An objective lens system for microscopes comprising a first positive lens, a second positive meniscus lens, a third negative lens, a fourth positive meniscus lens and a fifth positive meniscus lens, and said lens system having the following numerical data:

    ______________________________________                                         f = 1             NA = 0.25   β = -9.999                                  WD = 0.4083       Petzval sum 0.2                                              r.sub.1 = -1.3336                                                                         d.sub.1 = 0.0964                                                                          n.sub.1 = 1.755                                                                            ν.sub.1 = 52.4                            r.sub.2 = -0.5108                                                                         d.sub.2 = 0.0296                                                    r.sub.3 = 0.3588                                                                          d.sub.3 = 0.1079                                                                          n.sub.2 = 1.64                                                                             ν.sub.2 = 60.2                            r.sub.4 = 1.1284                                                                          d.sub.4 = 0.3806                                                    r.sub.5 = -0.2050                                                                         d.sub.5 = 0.1332                                                                          n.sub.3 = 1.80518                                                                          ν.sub. 3 = 25.4                           r.sub.6 = ∞                                                                         d.sub.6 =  0.0127                                                   r.sub.7 = -1.3245                                                                         d.sub.7 = 0.2177                                                                          n.sub.4 = 1.62299                                                                          ν.sub.4 = 58.2                            r.sub.8 = -0.4754                                                                         d.sub.8 = 0.0289                                                    r.sub.9 = 36.3549                                                                         d.sub.9 = 0.1387                                                                          n.sub.5 = 1.6425                                                                           ν.sub.5 = 58.4                            r.sub.10 = -.06668                                                             ______________________________________                                    

wherein the reference symbol f represents focal length of the entire lens system as a whole, the reference symbols r₁ through r₁₀ designate radii of curvature on the respective surfaces of the lenses, the reference symbols d₁ through d₉ denote thicknesses of the respective lenses and the airspaces therebetween, the reference symbols n₁ through n₅ represent refractive indices of the respective lenses and the reference symbols ν₁ through ν₅ designate Abbe's numbers of the respective lenses.
 3. An objective lens system for microscopes comprising a first positive lens, a second positive meniscus lens, a third negative lens, a fourth positive meniscus lens and a fifth positive meniscus lens, and said lens system having the following numerical data:

    ______________________________________                                         f = 1             NA = 0.25   β = -10.0                                   WD = 0.4122       Petzval sum 0.25                                             r.sub.1 = 0.7385                                                                          d.sub.1 = 0.0976                                                                          n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.6                            r.sub.2 = -0.8133                                                                         d.sub.2 = 0.0296                                                    r.sub.3 = 1.1096                                                                          d.sub.3 = 0.1065                                                                          n.sub.2 = 1.691                                                                            ν.sub.2 = 54.8                            r.sub.4 = 5.9537                                                                          d.sub.4 = 0.2661                                                    r.sub.5 = -0.2321                                                                         d.sub.5 = 0.1325                                                                          n.sub.3 = 1.84666                                                                          ν.sub.3 = 23.9                            r.sub.6 = ∞                                                                         d.sub.6 = 0.0138                                                    r.sub.7 = -0.4858                                                                         d.sub.7 = 0.2189                                                                          n.sub.4 = 1.618                                                                            ν.sub.4 = 63.4                            r.sub.8 = -0.3832                                                                         d.sub.8 = 0.0849                                                    r.sub.9 = 2.8955                                                                          d.sub.9 = 0.1159                                                                          n.sub.5 = 1.618                                                                            ν.sub.5 = 63.4                            r.sub.10 = -0.8358                                                             ______________________________________                                    

wherein the reference symbol f represents focal length of the entire lens system as a whole, the reference symbols r₁ through r₁₀ designate radii of curvature on the respective surfaces of the lenses, the reference symbols d₁ through d₉ denote thicknesses of the respective lenses and the airspaces therebetween, the reference symbols n₁ through n₅ represent refractive indices of the respective lenses and the reference symbols ν₁ through ν₅ designate Abbe's numbers of the respective lenses.
 4. An objective lens system for microscopes comprising a first positive lens, a second positive meniscus lens, a third negative lens, a fourth positive meniscus lens and a fifth positive meniscus lens, and said lens system having the following numerical data:

    ______________________________________                                         f = 1             NA = 0.25   β = -10.0                                   WD = 0.4187       Petzval sum 0.25                                             r.sub.1 = 3.6219                                                                          d.sub.1 = 0.0988                                                                          n.sub.1 = 1.7859                                                                           ν.sub.1 = 44.1                            r.sub.2 = -0.4897                                                                         d.sub.2 = 0.0305                                                    r.sub.3 = 0.3711                                                                          d.sub.3 = 0.1109                                                                          n.sub.2 = 1.6935                                                                           ν.sub.2 = 53.3                            r.sub.4 = 0.3933                                                                          d.sub.4 = 0.2297                                                    r.sub.5 = -0.2429                                                                         d.sub.5 = 0.1368                                                                          n.sub.3 = 1.84666                                                                          ν.sub.3 = 23.9                            r.sub.6 = ∞                                                                         d.sub.6 = 0.0135                                                    r.sub.7 = -0.9266                                                                         d.sub.7 = 0.2235                                                                          n.sub.4 = 1.48749                                                                          ν.sub.4 = 70.1                            r.sub.8 = -0.3829                                                                         d.sub.8 = 0.0766                                                    r.sub.9 =  5.1828                                                                         d.sub.9 = 0.1497                                                                          n.sub.5 = 1.618                                                                            ν.sub.5 = 63.4                            r.sub.10 = -0.7975                                                             ______________________________________                                    

wherein the reference symbol f represents focal length of the entire lens system as a whole, the reference symbols r₁ through r₁₀ designate radii of curvature on the respective surfaces of the lenses, the reference symbols d₁ through d₉ denote thicknesses of the respective lenses and the airspaces therebetween, the reference symbols n₁ through n₅ represent refractive indices of the respective lenses and the reference symbols ν₁ and ν₅ designate Abbe's numbers of the respective lenses. 